repro, status: config file error: Unsupported URL type b''://

UPDATE (@shcheklein )

See this fast way to reproduce and the summary of the issue: https://github.com/iterative/dvc/issues/6530#issuecomment-913818383

Bug Report

Description

I just upgraded DVC to version 2.6.4 and all of a sudden get this error with the same dvc.yaml file which worked fine previously. Note that while running these commands, another DVC process was running.

Reproduce

$ dvc status dvc.yaml
ERROR: config file error: Unsupported URL type b''://
$ dvc repro dvc.yaml --dry
ERROR: configuration error - config file error: Unsupported URL type b''://

Expected

Environment information

Output of dvc doctor:

$ dvc doctor
DVC version: 2.6.4 (conda)
---------------------------------
Platform: Python 3.9.6 on Linux-3.10.0-1160.15.2.el7.x86_64-x86_64-with-glibc2.17
Supports:
	http (requests = 2.25.1),
	https (requests = 2.25.1),
	s3 (s3fs = 2021.8.0, boto3 = 1.17.106)
Cache types: hardlink, symlink
Cache directory: xfs on /dev/md124
Caches: local
Remotes: s3, s3
Workspace directory: xfs on /dev/md124
Repo: dvc (subdir), git

Also observe this issue with DVC 2.5.4 after downgrading again:

> dvc doctor
DVC version: 2.5.4 (conda)
---------------------------------
Platform: Python 3.9.6 on Linux-3.10.0-1160.15.2.el7.x86_64-x86_64-with-glibc2.17
Supports:
	http (requests = 2.25.1),
	https (requests = 2.25.1),
	s3 (s3fs = 2021.6.1, boto3 = 1.17.49)
Cache types: hardlink, symlink
Cache directory: xfs on /dev/md124
Caches: local
Remotes: s3, s3
Workspace directory: xfs on /dev/md124
Repo: dvc (subdir), git

Additional Information (if any):

[schuhschuh]

I think I just found the cause of this issue. I added a print statement of stage and deps arguments passed to fill_stage_dependencies() and discovered that the deps list included a boolean False value. This was caused by the following in the dvc.yaml:

stages:
  stage_name:
    cmd: ...
    deps:
      - ${eval.model_path}

where eval.model_path is set in the params.yaml file. I set this to false in order to indicate that the model to be evaluated is a dummy model without trainable parameters (used as a reference for comparison). Removing this line from the dependencies resolved the issue.

It would probably make sense to check whether the arguments are valid file path strings to produce a more helpful error message.

[dberenbaum]

I just upgraded DVC to version 2.6.4 and all of a sudden get this error with the same dvc.yaml file which worked fine previously.

@schuhschuh Can you clarify whether you still expect this pipeline to run as is? I want to make sure we’re addressing your initial question, since it seems like at this point all of the issues found are about error handling, and some error was expected here since your dependency resolved to nothing.

1. The obvious one - we don't do the schema check after we apply the value as we do for the `dvc.yaml`. Should we do a separate `dvc.lock` schema check pass as we do for `dvc.yaml`? cc @skshetry

👍 I think we can leave this issue open to address validating the schema after applying the values.

2\. Error - cryptic and not useful. It took a lot of time and effort to figure out what's going on because of this.

Combined with the concerns about the stack trace, this seems like a discussion that might extend outside of this ticket about how that code is organized, but honestly I don’t have a lot of context without digging deeper. @skshetry What do you think?